Beam current-density dependence of the polarization of emission lines from foil-excited atoms: Beam dose dependent or field dependent

摘要

We have observed linearly polarized components of the foil-excited hydrogen Balmer alpha line and the neutral helium 2(1)P-3(1)D line from beams of 5-55 mu A/cm(2) current density at 150 keV. The intensities and the linear Stokes parameter of both the lines changed with the total beam charge density irradiated to the carbon foil (beam dose) and then saturated. These changes are attributed to changes of the state of the carbon foil caused by the irradiation by the ion beam. The dose dependence of the linear Stokes parameter was fitted with an exponential curve. The values at saturation for both the lines showed an increase with an increase in the current density, which is similar to the previous reports. The initial value for the helium line depended little on the beam current density, while that for the hydrogen line showed substantial increase. Both the behaviors are consistent with the explanation in terms of the Stark effect by the macroscopic electric field of the order of 10 V/cm extending downstream from the foil. [References: 17]